Concurrent flow

Spray Drying and Agglomeration. Most instant coffee products are spray-dried. Stainless steel towers with a concurrent flow of hot ak and atomized extract droplets are utilized for this purpose. Atomization, through pressure nozzles, is controUed based on selection of the nozzles, properties of the extract, pressures used, bulk density, and capacity requkements. Low inlet ak temperatures (200—280°C) are preferred for best flavor quaHty. The spray towers must be provided with adequate dust coUection systems such as cyclones or bag filters. The dried particles are coUected from the conical bottom of the spray drier through a rotary valve and conveyed to bulk storage bins or packaging lines. Processors may screen the dry product to... 

The final selection was a tubular reactor with upward concurrent flow, with hquid holdup of 20 to 30 percent, and with residence times of 1.0 s for gas and 3 to 5 min for hquid. 

The concurrent flow of liquid and gas in pipe lines has received considerable study [33], [35], [37], [41], However, pressure drop prediction is not extremely reliable except for several gas pipe line conditions. The general determinadons of pressure drop for plant process lines can only he approximated. 

Specchia, V., and Baldi, G., Pressure drop and liquid hold-up for two-phase concurrent flow in packed beds. Chem. Eng. Sci. 32, 515-523 (1977). 

Concurrent flow flame spread, representing vertical or ceiling spread, e.g. combustible linings. 

Fraction of original coke remaining at entrance to ith zone oKJ JUjyVeFe, r > 0 for concurrent flow, T < 0 for countercurrent flow... 

But this is not the case with a floating-head exchanger. The tube-side fluid reverses direction in the floating head. It has to. There is no way to attach the tube-side outlet nozzle to the floating head. It is a mechanical impossibility. So we bring the tube-side fluid back to the top half of the channel head. So, half of the tubes are in countercurrent flow with the shell-side flow. And that is good. But the other half of the tubes are in concurrent flow with the shell-side flow. And that is bad. 

Concurrent flow of liquid and gas can be simulated by the homogeneous model of Section 6.8.1 and Eqs. 6.109 or 6.112, but several adequate correlations of separated flows in terms of Lockhart-Martinelli parameters of pipeline flow type are available. A number of them is cited by Shah (Gas-Liquid-Solid Reactor Design, McGraw-Hill, New York, 1979, p. 184). The correlation of Sato (1973) is shown on Figure 6.9 and is represented by either... 

Figure 6.9. Pressure drop gradient and liquid holdup in liquid-gas concurrent flow in granular beds. [Sato, Hirose, Takahashi, and Toda, J. Chem. Eng. Jpn. 6, 147-152 (1973)]. (a) Correlation of the two phase pressure drop gradient A P/L, = 1.30 + 1.85Y-0 85. (b) Correlation of frictional holdup hL of liquid in the bed a, is the specific surface, 1/mm, d is particle diameter, and D is tube diameter, h, - 0.4a]/3Y 22.

FIGURE 3.7 Schematic of concurrent flow flame spread. 

Depending on the gas and liquid residence times required, the reactor could be operated horizontally or vertically with either downflow or upflow. Weikard (in Ullmann, Enzyklopaedie, 4th ed., vol. 3, Verlag Chemie, 1973, p. 381) discusses possible reasons for operating an upflow concurrent flow tubular reactor for the production of adipic acid nitrile (from adipic acid and ammonia). The reactor has a liquid holdup of 20 to 30 percent and a residence time of 1.0 s for gas and 3 to 5 min for liquid. 

In recent years, the process has been modified to increase the yield of lower olefines, too. Continually improved since then, especially in the mid-1960s with the replacement of the original silica-alumina catalyst by a zeolite. The catalyst is now typically a zeolite Y, bound in a clay matrix. The feed is vaporized and contacted in a pipeline reactor with concurrently flowing microspheroidal catalyst particles. The catalyst is then separated from the hydrocarbon products and is continuously regenerated by burning off the coke in a fluidized bed. The process is licensed by UOP several hundred units are in operation worldwide. See also HS-FCC. 

Wilkinson D P etal., 1998, Electrochemical Fuel Cell Stack with Concurrent Flow of Coolant and Oxidant Streams, and Countercurrent Flow of Fuel and Oxidant Streams. US Patent 5,773,160. 

If the cooling is by countercurrent or concurrent flow of a fluid stream, the temperature Tc of the cooling stream will be governed by the equation... 

Fukano, T., Kariyasaki, A., and Kagawa, M. (1989) Flow Patterns and Pressure Drop in Isothermal Gas-Liquid Concurrent Flow in a Horizontal Capillary Tube, Proceedings of the 1989 ANS National Heat Transfer Conference, Philadelphia, Pennsylvania, Vol. 4, pp. 153-161. 

Or the cell may be operated in concurrent flow as shown in Figure 19.9, or in countercurrent flow as shown in Figure 19.10. 

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